1. Field of the Invention
This invention relates to the formation of color dyes by the reaction of color couplers with other dye-forming compounds and especially relates to the imagewise formation of color dyes in a photographic element. More particularly, the invention is concerned with alleviating the problem of partial inactivation of color couplers caused by adventitious reaction of the couplers with formaldehyde or a vinyl monomer such as styrene.
2. Description Relative to the Prior Art
It is well known to use silver halide photographic elements containing color couplers to form color photographic images by means of imagewise coupling reactions of the color couplers with oxidized primary aromatic amino color developing agents. The developing agents are oxidized by reaction with imagewise exposed silver halide.
Some of the color couplers incorporated in photographic elements are susceptible to total or partial inactivation caused by adventitious contact with vapors of formaldehyde or vinyl monomers between manufacture and processing of the elements. This sometimes occurs, for example, through contact of a photographic element with polluted air. This problem is well known in the photographic art, especially in relation to many pyrazolone color couplers which are used to form magenta dyes in photographic elements. Descriptions of pyrazolone color couplers can be found in many references along with descriptions of the preparation and use of photographic elements which contain such couplers. See, for example, U.S. Pat. Nos. 2,600,788; 2,772,161; 2,865,748; 2,933,391; 3,006,759; 3,062,653; 3,214,437; 3,253,924; 3,311,476; and 3,419,391 and the patents referenced therein, all of which are hereby incorporated herein by reference.
If a color coupler susceptible to this problem comes into contact with a large amount of formaldehyde, it can become totally inactivated; i.e., it will not couple at all with an oxidized primary aromatic amino color developing agent, and no dye will be formed during processing. However, it is more commonly the case that a photographic element will adventitiously come into contact with only smaller amounts of formaldehyde. When this occurs, color couplers susceptible to the problem may be only partially inactivated. Although the mechanism of partial inactivation is not well understood, it is known that a partially inactivated color coupler will still react with oxidized developing agent to form a dye, but the dye will exhibit a less-than-normal degree of spectral absorptivity. It is theorized that in such cases the reaction with formaldehyde has only partially inhibited the coupling reaction or has otherwise reacted with the color coupler to tie up color-forming sites and prevent full color formation when the coupler combines with oxidized developing agent to form a dye. Whatever the true explanation for this phenomenon, its effect is well known.
It is also known that the effect of partial inactivation can be substantially overcome if, after the photographic element is developed with a primary aromatic amino color developing agent, subjected to a development stop bath and then washed during processing, the element is treated with an aqueous bleaching solution comprising a very potent bleaching agent, such as potassium ferricyanide, which has a very strong oxidizing effect. Such a bleaching agent will overcome the partial inactivation of a color coupler by formaldehyde and cause the spectral absorptivity of the dye formed by reaction of the color coupler with oxidized developing agent to be increased.
However, in order to achieve compactness of processing apparatus and speed of photographic processing operations, it is desirable to omit baths such as stop baths and washing baths from between the color development and bleaching baths. In addition, while the bleaching bath (the main purpose of which is to oxidize silver image for easy removal) has in the past been followed by a separate fixing bath (to remove oxidized silver image and unexposed silver halide from the element), it is desirable and known to further increase compactness and speed by incorporating the bleaching agent and fixing agent into a single bleach-fix bath. These practices require that a mild oxidizing agent be used as the bleaching agent, because a strong oxidizing agent such as potassium ferricyanide would cause indiscriminate formation of dye in the element if stop and wash baths were omitted after development, and, if incorporated in the same solution with a fixing agent, a strong oxidizing agent would oxidize the fixing agent making it useless for its fixing function. To avoid these problems, it is desirable to use a mild oxidizing agent as the bleaching agent (e.g., a complexed form of ferric ion such as iron ammonium ethylenediaminetetraacetic acid). Unfortunately, such mild bleaches are incapable of overcoming the partial inactivation of color couplers by formaldehyde, and it has heretofore been thought that, in order to overcome such partial inactivation, further steps of re-bleaching with a potent oxidizer and then washing out the bleach would have to be used. However, this would once again slow the processing operation and require new, less compact processing apparatus, because of the additional baths which would have to be used; and, in addition, it would once again raise the environmental problems of disposing of noxious substances such as the ferricyanides.
Therefore, it is apparent that a need exists for a method of alleviating the partial inactivation of color couplers, which does not require increasing photographic processing time by adding new processing baths and which does not require that new, less compact processing apparatus be used in order to practice the method. The present invention provides a method which satisfies this need.